1. Field of the Invention
The present invention relates to a method for measuring implanted ion dosages in semiconductors, both in real time as well as off-line. A particular feature of the method is its quick turnaround time and the wide range of implanted ion dosages that it can handle.
2. Description of the Prior Art
Ion implant technology is widely used in the fabrication of integrated circuits. It is standard in the art to sample the incoming ion current during deposition, integrating said current so as to obtain a measure of total dosage. It is, however, also necessary to obtain a direct measurement of the amount of material that was actually deposited. The two principal methods currently in use for this are (a) Thermal Wave and (b) Implanted Si Wafer.
The Thermal Wave employs a film of SiO2 as the monitoring medium for the implanted ions. While it has a cycle time of about a 1/2 hour, this method is limited to measuring ion concentrations in the range of 1.times.10E11 to 1.times.10E13/sq. cm. It cannot be used for sheet densities higher than this because the structure tends to self anneal (and thus invalidate the subsequent measurement) at the higher ion fluxes that are needed to reach these higher densities.
The Implanted Si Wafer is based on the measurement of electrical sheet resistance in the silicon itself. The method works best in the range of 1.times.10E13 to 1.times.10E16/sq. cm., however it involves a number of steps after ion implantation, such as heat treatment, oxide removal, etc. resulting in a cycle time that is in excess of half a day. In U.S. Pat. 5,217,907, May 1995, Bulucea et al. describe a probe for measuring sheet resistance, but the method is general and not related to ion implanted material as such.
Jasper, in U.S. Pat. No. 5,185,275, Feb. 1995, describes a method for measuring ion implantation dosages in gallium arsenide by using a silicon wafer as a monitor and then relating measurements made on the silicon to ion dosages in the gallium arsenide. This method suffers from the same disadvantages as other silicon based ion implant monitors as has already been discussed above.